Fragmentation
Table of Contents

Papers

2019 - J. Phys. Chem. A - 1,2,3,4-Tetrahydronaphthalene

This paper uses experiments (CID, VUV-Induced Dissociation) and calculations (DFT, RRKM) to investigate the dissociation of one system (Tetralin, C10H12 which is naphthalene+4H).

2019 - J. Phys. Chem. A - C2H2 loss

This paper is a computational study on the C2H2 loss from the ions of naphthalene, anthracene, phenanthrene, tetracene, and pyrene.

2015 - Phys. Rev. A - Role of hydrogenation in pyrene C16H10 fragmentation

The MD simulations were performed to simulate collisions between (hydrogenated) pyrene and He using the reactive Tersoff potential.

For Mass spectra for collisions between $C_{16}H_{10+m}^+$ (m = 0, 6, 16) and He at 110 eV center-of-mass energy, the major product is still their intact parent ion.

2014 - Phys. Rev. Lett. - Dissociation of hydrogenated coronene C24H12

The paper is organized as follows:

I don't understand something in this paper:

This paper didn't consider the possibility of CxHy loss and further hydrogenation (> 7H). Only one PAH molecule coronene is not enough to say that the hydrogenation can protect PAHs.

IRMPD review

This review provides an overview of the infrared spectroscopy of mass-selected gas-phase molecular ions (mainly polycyclic aromatic hydrocarbons, PAHs).

IRMPD

At a given lasing frequency, the IRMPD process only occurs when the IR irradiation is matching an IR active mode of the species under investigation. Recording the IRMPD efficiency as a function of IR wavelength results thus in an IR spectrum.

Energy

IRMPD typically requires the absorption of tens to hundreds of photons. The photon energy at 10 μm wavelength (1000 cm-1) is 0.12398 eV, thus the total energy needed is from 1.24 eV to 12.4 eV. Most aromatic systems have an ionization potential ranging from 7 to 8 eV.

Time scale

FELIX produces radiation in so-called macropulses, typically 5μs long, which consist of a train of 0.1–10 ps long micropulses. The micropulses are spaced by 1 ns. At room temperature, IVR lifetimes of aromatic molecules are typically much less than 1 ns.

IR calculation

B3LYP with a double zeta basis set is the recommended method here. It cites other old papers to say that this level of theory is able to give a good description of both geometries and vibrations. Only harmonic approximation of considered here, of which the resulting spectrum is a linear absorption spectrum. DFT calculated harmonic frequencies were uniformly scaled with a factor of 0.96 to account for anharmonicity as well as for experimental redshifting of bands caused by multiple photon excitation. This may differ from the experimentally obtained IRMPD spectrum where the multiple photon excitation mechanism matters. Nonetheless, despite these discrepancies for individual species, the general agreement between the experimental IRMPD spectra and the DFT computed linear absorption spectra is reasonably good.

General IR features of PAHs:

Dynamics

It is possible to describe the dynamical effects of IRMPD qualitatively with the presence of following difficulties:

MISC

First paper about IRMPD of cationic PAHs